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	<title>Document</title>
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		p{color:red;}
		#father>p{color: blue;}
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	<div id="father">
	<p>我是father的子元素，我是蓝色的</p>
	<div id="son">
		<p>我是father的孙子辈，我是红色的</p>
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	<p>我是father的兄弟，我是红色的</p>
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